Such organizations would make contingency plans to divert threatening near-Earth objects, and recommend how to proceed when those plans actually have to come into play. But the final decision to take action should be left up to the U.N. Security Council, the panel says.

The call to action, issued last Thursday, is the result of a three-year process spearheaded by the Association of Space Explorers - and particularly by Apollo 9 astronaut Rusty Schweickart, chairman of the association's committee on near-Earth objects, or NEOs.

One bad cosmic collision can ruin your whole day - or eon, as the dinosaurs discovered 65 million years ago. Based on Earth's impact history, scientists estimate that the planet suffers a hit capable of destroying civilizations every 500,000 to a million years on average - the so-called "background risk" for a NEO strike.

We're not facing any known NEO threat right now, but every once in a while a space rock comes along that gives the scientists pause, at least until its orbit can be defined with greater accuracy. It was that way with the asteroid 1997 XF11 a decade ago, and with the asteroid Apophis a couple of years ago.

The worries about Apophis have receded, but Schweickart told me we can expect many more worries to crop up as new observatories focus on NEOs in the years to come.

Software billionaire (and space passenger) Charles Simonyi, one of the backers of the $400 million Large Synoptic Survey Telescope, said during this month's congress of the Association of Space Explorers that the instrument will produce a torrent of astronomical data.

"In the first week, we will see more data from this telescope than all the telescopes in humanity up to that point," Simonyi said.

That's likely to produce significantly more observations of near-Earth objects - space rocks that may not be as big as the one that killed the dinosaurs, but could still wreak havoc on cities if they happened to be on a collision course, Schweickart said.

"In 10 or 15 years, 6,000 [near-Earth objects] is going to become 300,000 or more. The 200 with some probability of impact is going to become 6,000 to 10,000. The two or three of elevated concern is going to go to 100 or more," he said.

Who will sift through all those reports and figure out what to do with them? The scientific community has been pretty good about focusing on the potential close encounters, and so far the chances of catastrophe have been diminished in every case. But one of these days, scientists could come across a "cosmic Katrina" that doesn't go away.

The recommendations drawn up by the Panel on Asteroid Threat Mitigation, set up by the association's NEO committee, addresses how to prepare for that eventuality. The panel recommends that the United Nations set up three new organizations:

The Information, Analysis and Warning Network would coordinate the various ground-based and space-based that detect near-Earth objects. The network would analyze NEO orbits and establish criteria for issuing collision warnings.

The Mission Planning and Operations Group would draw upon the expertise of spacefaring nations to work out the best strategies for deflecting a threatening near-Earth object.

The U.N. NEO Threat Oversight Group would oversee the other groups and figure out what level of threat would merit international action. If a potential threat rose to that level, the group would develop recommendations for consideration by the U.N. Security Council.

Why get the U.N. involved? Why not just leave it to NASA, or the Defense Department, or the space and defense agencies of other countries? Schweickart pointed out that acting on a potential threat carries international risks. Efforts to change the incoming asteroid's path may actually increase the risk for some Earthlings. For example, in the process of shifting the collision path away from a direct hit on New York, a deflection effort could put Russia in the asteroid's sights.

"In the process of shifting the trajectory off the earth, it will move across the earth before it reaches the edge," Schweickart explained. "That is hopefully a temporary risk that is very, very low, if you do it correctly. But in that process, you've got the transitional issue."

That's why the expert panel recommends that the United Nations set up a system now, before the issue becomes a political hot potato (or a hot potato-shaped asteroid).

Schweickart said that the report has just been delivered to one of the action teams for the U.N. Committee on the Peaceful Uses of Outer Space, starting the ball rolling for consideration of the panel's recommendations. "Nothing happens in the United Nations without a very structured procedure, and nothing happens fast," he said.

He said it may take several years for the report to churn its way up through the U.N. space committee for action. "These things take time," Schweickart admitted, "but once they get in the front end of the process, they end up in the back end of the process."

The United Nations could decide to do nothing at all, but Schweickart hopes the world body will create a system as authoritative about cosmic threats as the Intergovernmental Panel on Climate Change is about global warming.

"We are not talking about the United Nations forming a space program," he insisted. "The United Nations needs to be involved in coordinating a response through the international community. ... You can't have every Tom, Dick and Harry or Susie saying, 'Oh, here's one coming at us, there's going to be a hit.'"

So does Schweickart, who has served in a variety of business and government roles after leaving NASA, aspire to become the world's asteroid czar? Not on your life. He'll be traveling around the world, trying to garner support for the asteroid crisis plan, but he doesn't see this as a lifelong quest.

"I see myself down the line as being out of the game, ASAP!" the 72-year-old said good-naturedly. "I've put in seven years of retirement, with no compensation, to get it this far. I'm looking forward to being back with my family, being on the golf course and doing all the things you're supposed to be doing when you're retired."

Schweickart's colleagues on the Association of Space Explorers' NEO committee are all former astronauts and cosmonauts: Sergei Avdeyev and Viktor Savinykh of Russia, Chris Hadfield of Canada, Thomas Jones and Edward Lu of the United States, and Dorin Prunariu of Romania.

Members of the Panel on Asteroid Threat Mitigation include:

Adigun Ade Abiodun, Nigeria, founder of the African Space Foundation.

Vallampadugai Arunachalam, India, chairman of the Center for Study of Science, Technology and Policy.

Roger-Maurice Bonnet, Switzerland, president of the Committee on Space Research.

Sergio Camacho-Lara, Mexico, secretary-general of the Regional Center for Space Science and Technology Education in Latin America and the Caribbean.